Lock-release gravity currents propagating over roughness elements

The influence of bottom roughness on the development of lock-release gravity currents is investigated through laboratory experiments using Particle Image Velocimetry. The bottom roughness is represented by arrays of vertical LEGO bricks with a constant spacing while varying λ, the relative height of the roughness elements to the gravity current depth. Depending on λ, the roughness elements may affect the gravity current propagation: for small λ the current behaves like moving over a smooth bottom, while for larger λ the propagation speed is reduced and the internal structure of the current, including both the head and the tail, is significantly modified. As λ increases, stronger recirculation areas between the roughness elements develop interacting with the overlying layer and giving rise to small-scale vortical structures of opposite sign within the whole depth of the current. The additional drag force induced by the bottom roughness adds significant complexity to the flow dynamics and modifies the characteristics of the current.